1. Field of the Invention
The present invention relates generally to synchronization of data in a data processing system and more particularly to the detection of a missing clock pulse for accurate discrimination between clock and data signals by means of a simplified missing clock detection circuit.
In data processing equipment wherein data is recorded on a recording medium such as magnetic tape, drum or disc, it is generally known to detect missing clock pulses by means of complex circuitry such as a phase locked loop, which causes a variable frequency oscillator to synchronize with the clock while at the same time generating a pulse upon detection of the missing clock to compensate for such occurrence. The present invention inserts a digital code at the missing clock location to enable distinct locations of missing clocks to be recorded for later decoding.
2. Description of the Prior Art
Generally, in recording digital data onto or reading data from a recording medium, such as a magnetic disc, the relative position of the data on the recording medium must be accurately and rapidly determinable. One technique for recording data for accurate recovery is the recording alternately of clock and data bits on the medium. The phase locked loop detectors of the prior art, as previously mentioned, require both an internal oscillator and complex circuitry synchronizing the oscillator with the recorded clock.
U.S. Pat. No. 3,405,391 of the prior art describes a system for reading magnetically recorded double frequency coded data with means for detecting and separating the clock bits from the data bits. In the present invention, data which indicates the position of data is discriminated from general recorded data in that it is recorded in the missing clock signal bit location. The delay circuitry of the referenced patent is not required by the present invention. Other prior art methods of data synchronization and missing bit detection are disclosed by U.S. Pat. Nos. 3,641,526; 3,418,585; 3,382,492; and 2,780,670.